1. Field of the Invention
The present invention relates to a video signal correcting device for correcting the non-presence of an analog video signal or the so-called drop-out.
2. Description of the Related Art
A conventional drop-out correcting circuit is constructed as is shown in FIG. 2. The level of the envelope of an FM analog video signal inputted through an input terminal 1 is detected by an envelope detector 2 and is led to a comparator 3. The comparator 3 delivers a drop-out detecting pulse DOC to an analog switch 4 when the level of the envelope becomes lower than a voltage of a power source 3'. To the analog switch 4, a signal delayed by 1H (horizontal period) by a delay line 7 and a present signal are inputted in such a manner that the analog switch 4 replaces a signal before 1H with the drop-out part by the drop-out detecting pulse DOC so as to correct the non-presence of the signal. Further, such a device are constructed in such a manner that the signal are demodulated in a demodulator 5 and then converted into a digital signal by an A/D converter 6 to be stored in an image memory 8. In case of such a construction, defects remain in an image signal very often when the analog switch 4 is changed over at the start and the end of the drop-out. Furthermore, it is very difficult to match the level of a signal having passed the 1H delay line 7 with that of a signal not having passed the delay line 7.
Further, a signal before 1H is simply replaced with the drop-out part, so that when the drop-out takes place at a position which is hardly relative to the signal before 1H, a good correction cannot be obtained, which is inconvenient.